Heat mat 5 watts

Heat mat.
adjustable by twist button.
5 watts.
EU plug.

Place the mat on the outside of your encloser, best on the side or back.
Better not on the bottom unless heat can be released, this because your glass could burst, besides that it is unnatural for the animal as they will dig down to cool down, which is not possible if the heat is coming from the bottom.
Best isolate on the outside with radiator foil.